Wireless networks have experienced increased development in the past decade. One of the most rapidly developing areas is mobile ad-hoc networks. Physically, a mobile ad-hoc network includes a number of geographically-distributed, potentially mobile nodes sharing a common radio channel. Compared with other types of networks, such as cellular networks or satellite networks, the most distinctive feature of mobile ad-hoc networks is the lack of any fixed infrastructure. The network may be formed of mobile nodes only, and a network is created “on the fly” as the nodes come close enough to transmit with each other. The network does not depend on a particular node and dynamically adjusts as some nodes join or others leave the network.
Because of these unique characteristics, routing protocols for governing data flow within ad-hoc networks are required which can adapt to frequent topology changes. Two basic categories of ad-hoc routing protocols have emerged in recent years, namely reactive or “on-demand” protocols, and proactive or table-driven protocols. Reactive protocols collect routing information when a particular route is required to a destination in response to a route request. Examples of reactive protocols include ad-hoc on demand distance vector (AODV) routing, dynamic source routing (DSR), and the temporally ordered routing algorithm (TORA).
On the other hand, proactive routing protocols attempt to maintain consistent, up-to-date routing information from each node to every other node in the network. Such protocols typically require each node to maintain one or more tables to store routing information, and they respond to changes in network topology by propagating updates throughout the network to maintain a consistent view of the network. Examples of such proactive routing protocols include destination-sequenced distance-vector (DSDV) routing, which is disclosed in U.S. Pat. No. 5,412,654 to Perkins; the wireless routing protocol (WRP); and clusterhead gateway switch routing (CGSR). A hybrid protocol which uses both proactive and reactive approaches is the zone routing protocol (ZRP), which is disclosed in U.S. Pat. No. 6,304,556 to Haas.
One challenge to the advancement of ad-hoc network development is that of security. In particular, since nodes are continuously entering and exiting a mobile ad-hoc network the task of ensuring that a node is a trustworthy source for data exchange can be difficult. Because of the early stage of development of ad-hoc networks and the numerous other challenges these networks present, the above routing protocols have heretofore primarily focused solely on the mechanics of data routing and not on such node authentication.
Some approaches are now being developed for performing node authentication within mobile ad-hoc networks. One such approach is outlined in a Capstone Proceeding paper by Nguyen et al. entitled “Security Routing Analysis for Mobile Ad Hoc Networks,” Department of Interdisciplinary Telecommunications, University Of Colorado at Boulder, Spring 2000. In this paper, the authors suggest using the U.S. Data Encryption Standard (DES) for encrypting plain text messages. For authentication, digital signatures and keyed one-way hashing functions with windowed sequence numbers are proposed.
More particularly, public-key encryption is used along with a one-way hash function to provide the digital signature. The sender uses the one-way hash function on the message and then encrypts the hash value with their private key. The message, along with the encrypted hash value, is sent to its destination. At the receiver, the hash value is also calculated based upon the message and is compared with the received hash value that was decrypted with the sender's public key. If they are the same, then the signature is authenticated.
Furthermore, rather than using a centralized (i.e., single) key management authority, a distributed public key management approach is suggested wherein a set of “trustworthy” nodes are designated that share sections of the public key management system. Each trusted node keeps a record of all public keys in the network, and the number of nodes needed to generate a valid signature is less than the total number of trusted nodes.
Another similar public/private key approach is discussed in an article by Zhou et al. entitled “Securing Ad Hoc Networks,” IEEE Network Magazine, vol. 13, no. 6, November/December 1999. This approach provides for a key management service which, as a whole, has a public/private key pair. All nodes in the system know the public key of the management service and trust any certificates signed using the corresponding private key. Nodes, as clients, can submit query requests to get other clients' public keys or submit update requests to change their own public keys. Internally, the key management service includes n special nodes called servers present within the ad-hoc network. Each server also has its own key pair and stores the public keys of all the nodes in the network. In particular, each server knows the public keys of other servers. Thus, the servers can establish secure links among themselves.
While the above papers address some aspects of implementing public/private key encryption and authentication in mobile ad-hoc networks, there are still further issues that remain to be addressed. For example, a would-be hacker could surreptitiously pose as an existing node in the network and lure a sending node to mistakenly send data thereto. Unless certain measures are taken, the hacker could act as a “man-in-the-middle” and forward authentication messages (and responses) to the intended destination. As a result, messages could still be altered and/or discarded, potentially crippling network communication.